A fan of the above-referenced type is known from document EP 1 404 008 A2, in which an electric motor with an external rotor is described which carries a fan wheel on its outer circumference. The stator has a stator insulation structure made of Duroplast, whereby a laminated stator core provided with stator windings is coated and simultaneously molded with the insulating material. As the rotor likewise encloses the stator, the heat in the region of the stator can considerably increase during operation.
The underlying problem of the present invention is to improve a fan of the above mentioned type such that effective cooling of the motor as well as favorable flow properties are ensured.
According to the present invention it is thus provided that, on the one hand, the rotor has ventilation openings in a front wall for a cooling air flow, and, on the other hand, it has projecting fins on a front wall axially opposite the ventilation openings which are arranged and distributed over the circumference, wherein a gap forms a passage between a circumferential rim of the rotor opposite the front wall and a flange-like stator carrier for the cooling air current flowing around the stator during operation. In this way, the ventilation opening of the rotor, on the one hand, and the passage between the circumferential rim of the rotor and the stator carrier, on the other hand, enable the flow of cooling air through the motor, whereby the cooling air flows around the stator through a circumferential gap located between it and the rotor. The flow direction depends on the design of the fan as well as, in particular, on which axial side a negative and/or positive pressure develops each time during operation. If, for example, negative pressure develops in the region of an axial suction opening in the case of a radial or diagonal fan, and if the rotor is facing the suction opening of the fan wheel with the front wall and the ventilation openings, cooling air is suctioned from the opposite side due to the negative pressure, i.e. the cooling air flows in through the passage at the circumferential rim of the rotor, flows around the stator and again flows out through the ventilation openings of the front wall. In the case of an axial fan, the flow direction of the cooling air depends on the actual conveying direction of the fan wheel, which in fact always flows in the opposite direction to the conveying direction.
The ventilation openings of the rotor and the projecting fins of the stator are in this case configured and arranged relative to one another such that during operation the motor cooling air is swirled in the region between the projecting fins of the stator and the ventilation openings of the rotor by means of a kind of “swirling effect.” The interaction between the ventilation openings of the rotor and the projecting fins of the stator preferably molded from the insulating material is especially important for the achieved heat dissipation (cooling) of the motor. In this way, the suctioned air, and therefore cooling air, flowing into the motor as a result of the negative pressure existing on one side of the fan during operation is swirled between the ventilation openings and the projecting fins—virtually according to the swirl principle, which, associated with the stator surface area which is enlarged by the projecting fins and acts as a convection surface, results in a very effective heat absorption (convection), i.e. the cooling air absorbs the motor heat and thus cools the motor and/or the stator. The cooling air also flows around the stator through the circumferential gap existing between the rotor and the stator and thereby further cools the stator.
Despite the cooling air current according to the present invention, the fan is also suitable for use in damp areas (for example for refrigeration and air-conditioning applications) because the encapsulated, i.e. pressed or overmolded, stator ensures a high IP degree of protection according to DIN EN 60529 and DIN 40050, Section 9.
In a further advantageous arrangement, the ventilation openings with a definite number of openings as well as the projecting fins with a definite number of fins are in particular arranged and distributed over the circumference in a radial symmetric manner. The number of openings and the number of fins should in any case be unequal and preferably also mutually prime. These unequal and preferably also mutually prime number of ventilation openings on the one hand, and of the projecting fins on the other hand, result in favorable, i.e. low, operating noise, in particular by avoiding the occurrence of resonance and/or rotational noise. In concrete terms, there are at least two—but preferably, however, a greater number of ventilation openings. Seven ventilation openings and six projecting fins are, for example, provided in an advantageous described embodiment. In that case, on account of their size, the ventilation openings jointly define an effective opening cross-section, whose relationship to the total, axially projected cross-sectional area of the rotor is between 10% and 30%.
It is further advantageous if each of the ventilation openings has a circumferential, nozzle-like opening rim that projects in the direction of the stator and with a maximum distance of about 4 mm extends out to the proximity of the projecting fins. These protruding opening rims still reinforce the “swirl effect” according to the present invention by interacting as “opposites” with the projecting fins; the cooling air is consequently swirled on both axially opposite sides between fins rotating relative to one another.
According to another aspect of the invention, in order to improve the flow properties, and namely, especially, for an arrangement as a radial fan, the invention provides that in the radial outer region of its front wall the rotor is converted into a cylindrical circumferential wall via a chamfered wall section, whereby the chamfered wall section and the longitudinal axis of the motor comprise a chamfer angle of 30° to 60°, preferably 50°. It is further advantageous if the front wall having the ventilation openings of the rotor is slightly tilted conically at a cone angle relative to the longitudinal axis, the cone angle being in the range of 60° to 80°, preferably 70°. By means of this particular feature it is possible that, in the case of a radial fan, even with a short axial dimension, i.e. a compact size, an enlarged inlet cross-section is formed in the region between an axial air inlet of the radial fan, the fan wheel configured as a radial wheel, and the rotor. This will be explained hereafter in more detail with reference to the drawings.